The present invention relates in general to a power supply having multiple outputs, each with a different DC voltage and more specifically to a resonant power supply wherein the multiple DC output voltages are regulated by changing the frequency of the voltage supplied to the resonant circuit.
It is well known in the art to used a DC to AC converter to supply voltage to a resonant circuit and to rectify the voltage across the resonant circuit so that a variable DC voltage may be obtained by varying the frequency of the DC to AC converter. It is also known that the resonant circuit may include a transformer, as shown for example by U.S. Pat. No. 4,504,895, issued Mar. 12, 1985 and assigned to the assignee of this application. Thus, by using multiple secondary windings (either separate windings or a multiply tapped secondary) a plurality of DC voltages can be obtained.
In the prior art, bifilar windings are typically used in the transformer secondary to maximize coupling between the secondary windings. However, as the number of bifilar windings increases, the winding procedure becomes complicated and thus expensive. Furthermore, if several pairs of windings are involved, bifilar windings lead to a bulky secondary and to voltage insulation problems. On the other hand, the close coupling of bifilar windings desirably suppresses voltage transients across the output rectifiers.
Accordingly, it is a principal object of the present invention to provide a multiple output resonant power supply having a single power converter and a single transformer.
It is a further object of the invention to provide a multiple output resonant power supply with a transformer having a non-bifilar wound secondary.
It is another object of the invention to provide accurate regulation of the DC output voltages of a multiple output resonant power supply.
It is another object of the invention to provide a DC power supply having high efficiency and low cost.